1. Field of the Invention
The present invention relates to an improved high power density solid oxide fuel cell which uses graded density for the anode, while still incorporating a relatively thick anode. More specifically, an anode of nickel and YSZ (zirconium oxide doped with yttrium oxide) is fabricated such that a major layer initially has about 80 percent by volume of NiO and a minor layer initially has about 60 percent by volume of NiO. The region containing about 80 percent by volume has a greater porosity which allows for easier transport of reactive gases. The invention permits the use of thicker and thus stronger anodes without sacrificing electrochemical performance. This invention makes it possible to achieve a high power density and at the same time have a thick electrode for durability and mechanical reliability greater than is observed in the fuel cells of the art.
2. Description of Related Art
A goal of current fuel cell research and technology is to provide a high power density and at the same time provide for improved durability and mechanical reliability.
Some patents of interest are as follows:
B. S. Baker in U.S. Pat. No. 4,329,403 discloses an electrolyte-electrode assembly for a fuel cell. The electrolyte component is adapted to exhibit a gradual transition in the coefficient of thermal expansion going from the anode of the inner electrolytic region and in going from the cathode region to the inner electrolyte region.
A. C. Khandkar in U.S. Pat. No. 5,171,645 discloses a graded electrolyte of zirconia and bismuth oxide. The strength and reduction resistance of zirconia with the high ionic conductivity of bismuth oxide form a superior oxygen ion-conducting electrolyte which is especially useful in fuel cells.
A. V. Virkar, et al. in U.S. Pat. No. 5,543,239 disclose an improved electrode design by incorporation of a porous layer of electrolyte material over the dense electrolyte creating an enhanced three phase (TPB) length. This design allows for fuel cells to have improved performance at lower operating temperatures.
H. L. Tuller, et al. in U.S. Pat. No. 5,509,189 disclose an electrochemical device which includes a solid electrolyte and solid electrode composed of materials having different chemical compositions and characterized by different electrical properties but having the same crystalline phase.
None of these U. S. patents teach or suggest the present invention.
All articles, patents, applications, references, standards and the like cited herein are incorporated by reference in their entirety.
It is desirable to have a high power density solid oxide fuel cell which has superior power densities and at the same time are more durable and mechanically reliable. The present invention provides such an improved fuel cell.